جستجوی مقالات مرتبط با کلیدواژه « بتن » در نشریات گروه « مهندسی شیمی، نفت و پلیمر »

One of the most important concerns of the drilling industry is reducing the negative impacts of drilling cuttings of oil-gas wells. The increasing growth of the oil industry and drilling of oil and gas wells led to large amounts of drilling waste. In this study, drilling cuttings in concrete as a substitute for part of the cement used in the construction industry has been investigated. In this study, the possibility of using drilling cuttings of formations of Bangistan group, including siltstone and sandstone, in concrete production has been evaluated as a substitute for part of the cement in concrete. For this purpose, laboratory studies have been conducted to quantify the compressive strength of concrete samples. The optimum use of drilling cuttings is 25%, which it reduces the total strength of concrete samples by 34%. In addition, the effect of air ash and silica fume additives on improving the compressive strength of concrete samples containing drilling cuttings has been investigated. The test results showed that the addition of these materials had a significant effect on increasing the compressive strength of concrete samples containing 25% of drilling cuttings so that the lost compressive strength is reduced from 34% to less than 2%.

Geometry of fractures including orientation, spacing, aperture and etc. are the influential parameters on permeability in rocks. In order to investigate the effect of spacing and orientation of fractures on permeability in laboratory scale, selecting proper sample is essential in terms of physical and mechanical properties. Therefore, in this study, two types of samples (concrete and fibrous fiber) were selected. Then, physical and mechanical parameters, which consist of density, water absorption, porosity, wave velocity, uniaxial compressive strength and permeability, were measured. The test results showed that the concrete sample is not appropriate sample for studying effect of fracture parameters on permeability due to high porosity, water absorption, permeability and brittle behavior of sample. However, the sample of fibrous fiber not only possesses the favorable physical and mechanical properties but also is suitable to create the fractures with different spacing and orientations as well as the same aperture owing to flexibility and ductile behavior.

Polycarboxylate ether superplasticizers are branch polymers with a main chain consisting of sodium salt of carboxylic and sulfonic acids ionic groups and polyethylene glycol arms. The efficiency of superplasticizer in concrete depends on the size of main chain, structures of repeating units, ion/branching ratio and density of branches with various side chain lengths. Superplasticizers are interacted and adsorbed on the surface of active particles present in the concrete. In the presence of polycarboxylate superplasticizers, hydration behavior of active sites and formation of crystals were investigated by Fourier transforms infrared spectroscopy, X-ray powder diffractometry and scanning electron microscopy. The results showed that adsorption of superplasticizers on the active species decreased the size of calcium hydroxide (CaOH) crystals and controlled the heat of hydration. Mechanical strengths, fluidity and fluidity retention of the concrete improved in the presence of superplasticizers. Furthermore, superplasticizers decreased the permeability of concrete and made its microstructure more compact.

Fire behaviour of ordinary (traditional), dense and SCC concretes is reviewed. Concrete is usually known as a material with good fire resistance. However, the mechanical resistance of concrete reduces with rising temperature because of chemical and dimensional changes, which can result in failure of the concrete element. Concrete has considerable amounts of water, which with high thermal capacity and low thermal conductivity of concrete can result in a low heat transfer rate from hot surface to bulk of concrete and hence delay the failure of component in fire. In contradictory, these characteristics can result in producing high vapour pressure in regions near the surface and spalling of concrete, which reduces the fire resistance of element, especially when the cover of reinforcing bars fails. The risk is much higher in dense concretes, like HSC and HPC. During the expose of concrete to fire, simultaneous heat and mass transfer phenomana cause that humidity trnsfers into internal layers. The vapor pressure will be rised in a region near the surface and reached to a maximum in a distance, which depends upon heating rate, moisture content, porosity, properties of materials, environment conditions, etc. The spalling will be occurred, if tensile strength is less than this pressure. Dense concrets may suffer from spalling in conditions that is not a risk for normal concretes. Self-compacting concretes also show different behaviour from other concretes at high temperatures. This is due to different compounds and high content volume of powders. The powders may result in a consirable decrease in fire resistance of concrete, because of low thermal stability or rise of packing of system, which can cause spalling in early stages of fire.